Electrosurgical generator and method for cross-checking output power

ABSTRACT

The functionality and the output power delivered are evaluated in an electrosurgical generator by calculating first and second values related to the output power delivered by using separate first and second computations. The two calculated values are compared, and an error condition is indicated when the two values differ by a predetermined amount. The separate computations, coupled with the other separate activities of measuring, averaging and sampling the output current and voltage measurements, serve as an effective basis for detecting errors caused by malfunctions or equipment failure. The error condition may be used to as a basis to terminate the output power delivery or indicate the error.

CROSS REFERENCE TO RELATED INVENTION

This is a division of application Ser. No. 10/299,988, filed Nov. 19,2002, which is now U.S. Pat. No. X,XXX,XXX.

This is also related to an invention for an Electrosurgical Generatorand Method with Multiple Semi-Autonomously Executable Functions,described in U.S. patent application Ser. No. 10/299,953, now U.S. Pat.No. Y,YYY,YYY, and for an Electrosurgical Generator and Method for CrossChecking Mode Functionality, described in U.S. patent application Ser.No. 10/299,952, now U.S. Pat. No. 6,875,210, both of which were filedconcurrently with application Ser. No. 10/299,988 and assigned to theassignee of the present invention. The subject matter of thesepreviously filed applications is incorporated herein by this reference.

FIELD OF THE INVENTION

This invention generally relates to electrosurgery. More specifically,the invention relates to a new and improved electrosurgical generatorand method that cross-checks the amount of the electrosurgical powerdelivered to assure proper functionality of the electrosurgicalgenerator and that the desired amount of electrosurgical power isdelivered during the surgical procedure.

BACKGROUND OF THE INVENTION

Electrosurgery involves applying relatively high voltage, radiofrequency (RF) electrical power to tissue of a patient undergoingsurgery, for the purpose of cutting the tissue, coagulating or stoppingblood or fluid flow from the tissue, or cutting or coagulating thetissue simultaneously. The high voltage, RF electrical power is createdby an electrosurgical generator, and the electrical power from thegenerator is applied to the tissue from an active electrode manipulatedby a surgeon during the surgical procedure.

The amount and characteristics of the electrosurgical energy deliveredto the patient is determined by the surgeon and depends on the type ofprocedure, among other things. For example, cutting is achieved bydelivering a continuous RF signal ranging up to relatively high power,for example 300 watts. Coagulation is achieved by rapidly switching theRF power on and off in a duty cycle. The coagulation duty cycle has afrequency considerably lower than the RF power delivered. However,during the on-time of each duty cycle, the electrical power is deliveredat the RF frequency. The power delivered during coagulation is typicallyin the neighborhood of approximately 40-80 watts, although powerdelivery as low as 10 watts or as high as 110 watts may be required.Simultaneous cutting and coagulation, which is also known as a “blend”mode of operation, also involves a duty cycle delivery of RF energy, butthe on-time of the duty cycle during blend is greater than the on-timeof the duty cycle during coagulation. Power is delivered at the RFfrequency because the frequency is high enough to avoid nervestimulation, thereby allowing the tissue to remain somewhat stationarywithout contractions caused by the electrical energy.

The electrosurgical generator must also have the capability to deliver arelatively wide range of power. The resistance or impedance of thetissue may change radically from point-to-point during the procedure,thereby increasing the power regulation requirements for theelectrosurgical generator. For example, a highly fluid-perfused tissue,such as the liver, may exhibit a resistance or impedance in theneighborhood of 40 ohms. Other tissue, such as the marrow of bone, mayhave an impedance in the neighborhood of 900 ohms. The fat or adiposecontent of the tissue will increase its impedance. The variablecharacteristics of the tissue require the electrosurgical generator tobe able to deliver effective amounts of power into all types of thesetissues, on virtually an instantaneously changing basis as the surgeonmoves through and works with the different types of tissues at thesurgical site.

These wide variations in power delivery encountered duringelectrosurgery impose severe performance constraints on theelectrosurgical generator. Almost no other electrical amplifier issubject to such rapid response to such widely varying power deliveryrequirements. Failing to adequately regulate and control the outputpower may create unnecessary damage to the tissue or injury to thepatient or surgical personnel. In a similar manner, failing toadequately establish the electrical characteristics for cutting,coagulating or performing both procedures simultaneously can also resultin unnecessary tissue damage or injury.

Almost all electrosurgical generators involve some form of output powermonitoring circuitry, used for the purpose of controlling the outputpower. The extent of power monitoring for regulation purposes variesdepending upon the type of mode selected. For example, the coagulationmode of operation does not generally involve sensing the voltage andcurrent delivered and using those measurements to calculate power forthe purpose of regulating the output power. However, in the cut mode ofoperation, it is typical to sense the output current and power and usethose values as feedback to regulate the power delivered.

In addition to power regulation capabilities, most electrosurgicalgenerators have the capability of determining error conditions. Theoutput power of the electrosurgical generator is monitored to ensurethat electrosurgical energy of the proper power content andcharacteristics is delivered. An alarm is generated if an error isdetected. The alarm may alert the surgeon to a problem and/or shut downor terminate power delivery from the electrosurgical generator.

Certain types of medical equipment controlled by microprocessors ormicrocontrollers utilize multiple processors for backup and monitoringpurposes. Generally speaking, one of the processor serves as a controlprocessor to primarily control the normal functionality of theequipment. Another one of the processors serves as a monitor processorwhich functions primarily to check the proper operation of the controlprocessor and the other components of the medical equipment. Using oneprocessor for primary control functionality and another processor forprimary monitoring functionality has the advantage of achievingredundancy for monitoring purposes, because each processor has theindependent capability to shut down or limit the functionality of themedical equipment under error conditions. Standards and recommendationseven exist for multiple-processor medical equipment which delineates theresponsibilities of the safety and monitoring processors.

SUMMARY OF THE INVENTION

The present invention has evolved from a desire to achieve a high degreeof reliability for monitoring purposes in a multiple-processorelectrosurgical generator. The present invention has also evolved fromrealizing that control and monitoring functionality, as well as thecomponents used for monitoring conditions, need to be cross-checked on acontinual and relatively frequently recurring basis to ensure properfunctionality in the context of the rapidly and widely varying outputrequirements of an electrosurgical generator. In addition, the presentinvention advantageously monitors output power in an electrosurgicalgenerator by using multiple processors not only for the purpose ofcontrolling the electrosurgical generator from an output powerregulation standpoint, but also for the purpose of checking properfunctionality of the processors and their other associated equipment ona general basis.

In accordance with these improvements, the present invention involves amethod of evaluating the functionality of an electrosurgical generatorand the electrosurgical output power delivered by the generator. A firstvalue related to the output power delivered is calculated using a firstcomputation, and a second value related to the output power delivered iscalculated using a second computation. The first and second values arecompared, and an error condition is indicated when the first and secondvalues differ by a predetermined amount. Preferably, separatemeasurements of the voltage and current of the power delivered are usedin performing the first and second computations, the first and secondvalues are average values calculated over different predeterminedperiods of time, and the two output current and the output voltagemeasurements are sampled at different sampling frequencies forcalculating the first value with the first computation. The separatecomputations of the first and second values, coupled with the otherpreferable separate activities of measuring, averaging and sampling theoutput current and voltage measurements, contribute an effective basisfor cross-checking the proper functionality and power output of theelectrosurgical generator, and taking action to prevent risks to thepatient from improper power delivery or other improper functionality ofthe generator under such error conditions.

Another method of evaluating the functionality and output powerdelivered, which also obtains the same benefits and improvements,involves activating the electrosurgical generator to deliver the outputpower, sensing the current and the voltage at first periodic intervalsto obtain a first set of measurements of the current and voltage of theoutput power delivered, sensing the current and the voltage at secondperiodic intervals to obtain a second set of measurements of the currentand voltage of the output power delivered, recording the first andsecond sets of measurements, deactivating the electrosurgical generatorto terminate the delivery of the output power, calculating a first valuerelated to the output power delivered from the first sets of recordedmeasurements by executing a first computation with the controlprocessor, calculating a second value related to the output powerdelivered from the second sets of recorded measurements by executing asecond computation with the monitor processor, comparing the calculatedfirst and second values to determine whether the calculated first andsecond values differ by a predetermined amount, and executing an errorresponse upon determining that the calculated first and second valuesdiffer by the predetermined amount.

The present invention also involves an improved electrosurgicalgenerator having the capability of evaluating its own functionality andthe output power delivered. A plurality of sensors sense current andvoltage of the output power delivered and supply current and voltagemeasurement signals related to the amount of current and voltage sensed.A control processor receives the current and voltage measurement signalsand performs a first computation based on the current and voltagemeasurement signals to derive power regulation feedback information andto derive a first value related to the output power delivered. A monitorprocessor receives the current and voltage measurement signals andperforms a second computation separate from the first computation toderive a second value related to the output power delivered. Acommunication path connects the control and monitor processors by whichto communicate information including the first and second values betweenthe processors. One of the control or monitor processors functions as acomparison processor to execute a comparison procedure for comparing thefirst and second values and delivering an error condition signal whenthe first and second values differ by a predetermined amount. Theelectrosurgical generator responds to an assertion of the errorcondition signal by either issuing an error indication and/orterminating the delivery of output power. Preferable features of theelectrosurgical generator include individual sensors for derivingindependent current measurement and independent voltage measurementsignals used in the two computations. Another preferable feature of theelectrosurgical generator is a direct memory access (DMA) technique ofreading digital forms of the current and voltage measurement signalsinto memory, and thereafter reading those signals from memory to performthe two computations. The separate computations, coupled with the otherpreferable individual measurements of the output current and voltage,permit the electrosurgical generator to cross-check its ownfunctionality and power output, and to take appropriate action toprevent risks to the patient if a discrepancy is detected.

A more complete appreciation of the present disclosure and its scope,and the manner in which it achieves the above noted improvements, can beobtained by reference to the following detailed description of presentlypreferred embodiments taken in connection with the accompanyingdrawings, which are briefly summarized below, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a multiple processor electrosurgicalgenerator incorporating the present invention.

FIG. 2 is a block diagram of a portion of an RF output section of theelectrosurgical generator shown in FIG. 1.

FIG. 3 is a block diagram illustrating signal and information flowduring a output power monitoring by one of the processors of theelectrosurgical generator shown in FIG. 1.

FIG. 4 is a flow chart for a procedure for generating information usedfor monitoring power output and creating information, executed by thecomponents shown in FIGS. 2 and 3 of the electrosurgical generator shownin FIG. 1.

FIG. 5 is a flow chart for a procedure for communicating, analyzing andresponding to the information generated by the procedure shown in FIG.4.

DETAILED DESCRIPTION

An electrosurgical generator 20, shown in FIG. 1, supplieselectrosurgical output voltage and output current at 22, which isconducted to an active electrode (not shown) for monopolar and bipolarelectrosurgery. Current is returned at 24 to the electrosurgicalgenerator 20 from a return electrode (not shown), after having beenconducted through the tissue of the patient. The generator is activatedto deliver the electrosurgical output power at 22 by an activationsignal supplied at 26. The activation signal 26 is asserted upon closinga switch on a handpiece (not shown) which supports the active electrodeand is held by the surgeon. The activation signal 26 may also beasserted from a conventional foot switch (not shown) which is depressedby foot pressure from the surgeon.

The electrosurgical generator 20 includes a system processor 30, acontrol processor 32, and a monitor processor 34. The system processor30 generally controls the overall functionality of the electrosurgicalgenerator 20. The system processor 30 includes nonvolatile memory (notshown) containing programmed instructions to be downloaded to the otherprocessors 32 and 34 to establish the functionality of the control andmonitor processors 32 and 34, as well as the entire functionality of theelectrosurgical generator 20. The processors 30, 32 and 34 communicatewith each other over a system bus 36. In general, the system processor30 supervises and controls, at a high level, the entire electrosurgicalgenerator 20.

The primary functionality of the control processor 32 is to establishand regulate the power delivered from the electrosurgical generator at22. The control processor 32 is connected to a high voltage power supply38, an RF amplifier 40, and an RF output section 42. The high voltagepower supply 38 generates a DC operating voltage by rectifyingconventional alternating current (AC) power supplied by conventionalmains power lines 44, and delivers the DC operating voltage to the RFamplifier 40 at 46. The RF amplifier 40 converts the DC operatingvoltage into monopolar drive signals 50 and bipolar drive signals 52having an energy content and duty cycle appropriate for the amount ofpower and the mode of electrosurgical operation which have been selectedby the surgeon. The RF output section 42 converts the monopolar andbipolar drive signals 50 and 52 into the RF voltage and currentwaveforms and supplies those waveforms to the active electrode at 22 asthe output power from the electrosurgical generator.

The basic function of the monitor processor 34 is to monitor thefunctionality of the high voltage power supply 38 and the RF outputsection 42, as well as to monitor the functions of the system processor30 and the control processor 32. If the monitor processor 34 detects adiscrepancy in the output electrosurgical energy, or a discrepancy inthe expected functionality of the system processor 30 or the controlprocessor 32, a failure mode is indicated and the monitor processor 34terminates the delivery of output electrosurgical energy from theelectrosurgical generator 20.

The processors 30, 32 and 34 are conventional microprocessors,microcontrollers or digital signal processors, all of which areessentially general purpose computers that have been programmed toperform the specific functions of the electrosurgical generator 20.

The electrosurgical generator 20 also includes user input devices 54which allow the user to select the mode of electrosurgical operation(cut, coagulation or a blend of both) and the desired amount of outputpower. In general, the input devices 54 are dials and switches that theuser manipulates to supply control, mode and other information to theelectrosurgical generator. The electrosurgical generator 20 alsoincludes information output displays 56 and indicators 58. The displays56 and indicators 58 provide feedback, menu options and performanceinformation to the user. The input devices 54 and the output displays 56and indicators 58 allow the user to set up and manage the operation ofthe electrosurgical generator 20.

The activation signals at 26 are applied from the finger and footswitches to an activation port 62. The system processor 30 reads theactivation signals 26 from the port 62 to control the power deliveryfrom the electrosurgical generator 20. The components 54, 56, 58 and 62are connected to and communicate with the system processor 30 by aconventional input/output (I/O) peripheral bus 64, which is separatefrom the system bus 36.

In order to continually monitor the power delivered, as well as toachieve a high degree of reliability and redundancy for safetymonitoring purposes, the control processor 32 and the monitor processor34 each independently calculate the power delivered from the RF outputsection 42. The independent power calculations are thereafter compared,by at least one of the three processors 30, 32 and 34, and if adiscrepancy is noted, the comparing processor signals the systemprocessor 30 of the discrepancy, and the power delivery from theelectrosurgical generator 20 is shut down and/or an error is indicated.

The power calculations performed by the control processor 32 are part ofthe normal functionality of the control processor in regulating theoutput power. The control processor 32 receives an output current signal70 and an output voltage 72 from the RF output section 42. The controlprocessor calculates the amount of output power by multiplying thecurrent and voltage signals 70 and 72 to obtain the power output. Themonitor processor 34 receives an output current signal 74 and an outputvoltage signal 76. The output current and voltage signals 74 and 76 arederived independently of the output current and voltage signals 70 and72, by separate current and voltage sensors. The monitor processor 34calculates the output power based on the output current and voltagesignals 74 and 76. The power-related calculations performed by thecontrol processor 32 and by the monitor processor 34 are not necessarilyperformed at the same frequency or at exactly the same time, althoughthe power calculations must be sufficiently related in time so as to becomparable to one another.

The separately-calculated power related information is periodicallycompared by one or more of the processors 30, 32 or 34, preferably ineither the system processor 30 or the monitor processor 34. To make thecomparison, the calculated power information is communicated over thesystem bus 36 to the processor which performs the comparison. If thecomparison shows similar power calculations within acceptable limits,proper functionality of the electrosurgical generator 20 is indicated.If the comparison shows dissimilar power calculations outside ofacceptable limits, safety related issues are indicated. Dissimilar powercalculations may indicate that one of the control or monitor processors32 or 34 is malfunctioning, or some of the components used in connectionwith the processors are malfunctioning, or a failure in one of thecurrent and voltage sensors which supply the current and voltage signals70, 72, 74 and 76, among other things. In general, the response to anissue indicated by a power calculation discrepancy will result inindication of an error condition and/or the termination of powerdelivery from the electrosurgical generator 20. Information will also besupplied to and presented at the displays 56 and indicators 58describing the error condition.

Each of the processors 30, 32 and 34 has the capability to exercisecontrol over the delivery of power from the electrosurgical generator.The monitor processor 34 and the system processor 30 assert enablesignals 78 and 79 to an AND logic gate 82. The control processor 30asserts a drive-defining signal 80 to the logic gate 82. Thedrive-defining signal 80 is passed through the logic gate 82 and becomesa drive signal 84 for the RF amplifier 40, so long as the enable signals79 and 80 are simultaneously presented to the logic gate 82. If eitherthe system processor 30 or the monitor processor 34 de-asserts itsenable signal 79 or 78, respectively, the logic gate 82 will terminatethe delivery of the drive signal 84, and the RF amplifier 80 will ceaseto deliver monopolar and bipolar drive signals 50 and 52, resulting interminating the delivery of electrosurgical power from the generator 20at 22. Because the control processor 32 develops the drive-definingsignal 80 to control the output power of the electrosurgical generator,the control processor 82 can simply de-assert the drive-defining signal80 to cause the electrosurgical generator to cease delivering outputpower. Thus, any of the processors 30, 32 or 34 as the capability toshut down or terminate the delivery of power from the electrosurgicalgenerator under conditions of significant discrepancies in theindependently-calculated power output by de-asserting the signals 79, 80or 82, respectively.

More details concerning the derivation of the output current and outputvoltage sense signals 70, 72, 74 and 76 are understood by reference toFIG. 2, which illustrates a portion of the RF output section 42 (FIG.1). The flow path for the monopolar electrosurgical current is through adelivery conductor 86, through series-connected current sensors 88 and90, through relays 92 and to one or more plug connectors 94, 96 or 98which are selected by the relays 92. The monopolar electrosurgicalcurrent flows from the plug connectors 94, 96 and 98 to the activeelectrode at 22. The return path for the monopolar electrosurgicalcurrent is from the electrical return electrode (not shown) at 24 to areturn plug connector 100 to which the return electrode (sometimesreferred to as a return pad) is connected. The return current flowsthrough a return conductor 102. Voltage sensors 104 and 106 areconnected between the delivery conductor 86 and the return conductor 102to sense the voltage at which the monopolar electrosurgical output poweris delivered.

The current sensor 88 delivers the output current sense signal 70 to thecontrol processor 32 (FIG. 1), and the current sensor 90 delivers theoutput current sense signal 74 to the monitor processor 34 (FIG. 1). Ina similar manner, the voltage sensor 104 delivers the output voltagesense signal 72 to the control processor 32 (FIG. 1), and the voltagesensor 106 delivers the output voltage sense signal 76 to the monitorprocessor 34 (FIG. 1). Arranged in this manner, the current sensors 88and 90, and the voltage sensors 104 and 106 supply their own sensesignals, independently of sense signals supplied by the other sensors.Any adverse functionality of one of the sensors will not thereforeaffect the functionality of the other sensors.

The flow path of the bipolar electrosurgical current is from a firstbipolar delivery conductor 108, through series-connected current sensors110 and 112 and to a bipolar output plug connector 114. The bipolarelectrosurgical current flows from the plug connector 114 to the activeelectrode at 22 and returns from the return electrode at 24. The returncurrent flows from the bipolar output plug connector 114 through asecond bipolar conductor 120. Voltage sensors 116 and 118 are connectedbetween the first and second bipolar delivery conductors 108 and 120 andtherefore sense the voltage at which the bipolar electrosurgical outputpower is delivered.

The current sensor 110 delivers the output current sense signal 70 tothe control processor 32 (FIG. 1), and the current sensor 112 deliversthe output current sense signal 74 to the monitor processor 34 (FIG. 1).In a similar manner, the voltage sensor 116 delivers the output voltagesense signal 72 to the control processor 32 (FIG. 1), and the voltagesensor 118 delivers the output voltage sense signal 76 to the monitorprocessor 34 (FIG. 1). Arranged in this manner, the current sensors 110and 112, and the voltage sensors 116 and 118 supply their own sensesignals, independently of sense signals supplied by the other sensors.Again, adverse functionality of one of the sensors will not thereforeaffect the functionality of the other sensors.

Only one set of the current sense signals 70 and 74 and only one set ofthe voltage sense signals 72 and 76 will be supplied when theelectrosurgical generator is operating in either the monopolar or thebipolar mode. In other words, it is not possible for the electrosurgicalgenerator to operate in both the monopolar and the bipolar modesimultaneously under normal operating conditions. Each of the sensors116, 118, 104, 106, 110, 112, 88 and 90 is preferably a conventionaltransformer.

The current sense signals 70 and 74, and the voltage sense signals 72and 76 are applied to and dealt with by the control processor 32 and themonitor processor 34, respectively, each in the similar manner shown inFIG. 3. The current and voltage sense signals 70 (74) and 72 (76) aresupplied from the RF output section 42 (FIGS. 2 and 1) to a conventionalanalog to digital converter (ADC) 122. The ADC 122 converts theinstantaneous values of the analog current and voltage sense signals 70(74) and 72 (76) into sample values at sampling intervals established bycontrol signals supplied by the microprocessor 32 (34). The samplevalues of the current and voltage sense signals 70 (74) and 72 (76) arestored in a conventional buffer memory 126 at sequential addressesestablished by a conventional direct memory access (DMA) controller 124.The ADC 122 and the DMA controller 124 operate on semi-autonomous basisto store the sample values of the current and voltage sense signals inthe buffer 126. One exemplary sampling technique that may be effectivelyemployed in the present invention is described in greater detail in thefirst above-identified U.S. patent application filed concurrentlyherewith.

After a predetermined number of sample values of the current and voltagesense signals 70 (74) and 72 (76) have been stored in the buffer 126,the microprocessor 32 (34) reads those values and thereafter calculatespower-related information. After reading the values of the current andvoltage sense signals from the buffer 126, the DMA controller 124replaces those values in the buffer 126 with new values supplied by theADC 122.

The power-related information is preferably root mean square (RMS)output power or some value related to RMS output power. One preferredtechnique for calculating the power-related information is for themicroprocessor 32 (34) to square each of the instantaneous sample valuesof the current and voltage sense signals 70 (74) and 72 (76), sum all ofthe squared current sample values, sum all of the squared voltage samplevalues, multiply together the sum of the squared voltage sample valuesand the sum of the squared current sample values, and take the squareroot of the product obtained from the multiplication. This example of acalculation is not true RMS power, because no step was performed todivide by the number of collected samples. However, the resultingpower-related information is directly related to RMS power because thenumber of samples taken and used in the calculation is the same. Othertypes of mathematical calculations may be performed to obtain thepower-related information in accordance with the present invention. Oneexemplary to calculation technique for determining power-relatedinformation is described in greater detail in the first above-identifiedU.S. patent application filed concurrently herewith. Other power-relatedinformation calculation algorithms can also be employed with the presentinvention.

Calculating power by obtaining a plurality of sample values over apredetermined time effectively integrates the power-related information.This is particularly advantageous in view of the typical manner in whichan electrosurgical generator is activated by the surgeon. The typicalactivation procedure is for the surgeon to depress the finger controlswitch or step on the foot switch only for a few seconds at a time toperform a series of relatively short and continually repetitive surgicalactions during the entire electrosurgical procedure. Collecting samplesover a relatively long period of time permits integration and long-timedigital filtering of the values resulting from each of these shortactivations as a type of filtering to eliminate anomalous effects.

With similar voltage and current sense signals, the control processor 32and the monitor processor 34 should each calculate almost the sameamount of power. Some small difference between the calculated values mayoccur due to timing considerations for each of the signals or slightdifferences in the sensors or in the signal paths for each of thesignals. Thus, the comparison looks for the two results to be almost thesame within an acceptable tolerance that may be determined empirically.

After performing the calculations, the results are stored in a memory128 or held in the processor performing the calculation. The memory 128is connected to the system bus 36 so that the results of thecalculations stored in the memory 128 can be read by one or more of theother processors which are also connected to the system bus 36.

To perform the comparison of the calculated power-related results, thecalculated power-related results are communicated over the system bus 36to the system processor 30 or to either the control processor 32 or themonitor processor 34 (FIG. 1). Either the system processor 30 or themonitor processor 34 (FIG. 1) should perform the comparison, to obtain aredundancy check on the operation of the control processor 32 (FIG. 1)which must make the calculation to regulate the output power. However,depending upon the capability of the control processor 32, it mayperform the comparison of the power-related information. The processorwhich performs the comparison, hereinafter referred to as the“comparison processor,” receives the calculated power information fromthe memory 128 of the control processor 32 and the monitor processor 34to perform the comparison.

An exemplary and more detailed explanation of the process flow orprocedure 150 used by the control and monitor processors 32 and 34 tocalculate the power-related information from the sampled current andvoltage values is shown in FIG. 4. The procedure 150 starts at step 152.At step 154 it is determined whether the electrosurgical generator hasbeen activated, by the delivery of the activation signal 26 (FIG. 1).Until activation, the procedure 150 waits at step 154. Once activationoccurs, either a timer is started or the current time (a start time) isrecorded, and shown at step 156. The processor is able to measure orcalculate the duration of the activation. The sample values of thecurrent and voltage signals are collected at step 158 until theelectrosurgical generator is determined to be de-activated at step 160.At step 158, the ADC 122 converts the analog values of the current andvoltage sense signals to their digital sampled values, and the DMAcontroller 124 stores the instantaneous sampled values generated by theADC 122 in the buffer memory 126 (FIG. 3). This occurs until theelectrosurgical generator is de-activated at step 160 or until thebuffer memory 126 is filled with samples. Upon deactivation at step 160,the collection of the sampled values (data) is stopped at step 162.Thereafter at step 164, the timer is stopped or the current time (a stoptime) is recorded.

If the time duration during which the electrosurgical generator wasactivated is not within a predetermined window of time, as determined atsteps 166 and 168, then the power-related information calculations arenot performed. Instead, the procedure 150 returns to step 154 to waitfor the next activation. In this manner, certain common events whichtypically do not involve the delivery of the electrosurgical powerduring an actual procedure will not result in an inadvertent,unnecessary shutdown of the electrosurgical generator. For example, somesurgeons momentarily short-circuit the output power terminals of theelectrosurgical generator to observe an arc as a technique fordetermining whether the electrosurgical generator is operating. Whilethis is not recommended procedure, it does indicate to the surgeon thatthe electrosurgical generator is working. Since there is no tissueresistance or impedance, the current and voltage sense signals currentand voltage sense signals 70 (74) and 72 (76) are anomalous. Suchanomalies could cause such a large discrepancy in the calculatedpower-related information such that, when the comparison is made, anerror is detected, when in fact, there was no actual error. Also, eitherthe control processor 32 or the monitor processor 34 may miss part orall of a power delivery event that is too short. In a similar manner,the maximum time duration of the predetermined window of time determinedat step 168 is used to obtain accurate samples during the activationtime by preventing inordinately long activations of the electrosurgicalgenerator from delivering so many sampled values of the sensed voltageand current to the buffer 126 (FIG. 3) to cause it to overflow.

Thus, the predetermined window of time, established at steps 166 and168, enables the procedure 150 to prevent an inadvertent shutdown of theelectrosurgical generator 20 in anomalous situations. The size of thewindow is selected based on an empirical data concerning of the typicalduration of most electrosurgical procedures, which usually fall within arange of minimum and maximum times (e.g. 0.5-5.0 seconds, respectively).The size of the buffer 126 and the sampling rate of the ADC 122 (FIG. 3)may also define the maximum time limit at step 168 over which data maybe collected, although the results of filling numerous buffers may alsobe accumulated if information is collected over a longer time period.The predetermined window of time is fixed by a minimum time, establishedat step 166, and a maximum time, established at step 168, and theseminimum and maximum times define the preferred time frame for which thepower-related information is obtained.

If the duration of the electrosurgical procedure is within thepredetermined window of time, as determined at steps 166 and 168, thenthe various calculations for RMS voltage, current and power areperformed at step 170. The power-related results of the calculations arethen sent, at step 172, to the comparison processor to perform thecomparison of the results. The procedure 150 then returns to step 154.

As an alternative to determining whether the activation of theelectrosurgical generator is within the predetermined window of time atsteps 166 and 168, the RMS calculations may be done by the control andmonitor processors regardless of the duration of the activation. In thiscase, the comparison processor makes a determination of whether toeliminate the comparison if the duration is outside the window.

An exemplary and more detailed explanation of a process flow orprocedure 200 for making the comparison between the calculatedpower-related information from the control and monitor processors, andresponding, is shown in FIG. 5. The procedure 200 starts at step 202. Atstep 204 a determination is made whether the electrosurgical generatorhas been de-activated. So long as deactivation exists, the procedure 200waits at step 204. Once activation occurs, the determination at 204 isaffirmative, and the calculated power-related information is read fromthe memories 128 (FIG. 3) of the control processor 32, at step 206, andfrom the memories 128 of the monitor processor 34, at step 208, orotherwise supplied by the two calculating processors. If either thecontrol processor or the monitor processor is the comparison processor,it may or may not actually store the results of the power calculationsin its associated memory 128, while performing the procedure 200.

At steps 210 and 212 respectively, it is determined whether the twocalculated results are within an acceptable tolerance of each other. Ifthe calculated result (C) from the control processor 32 is not greaterthan the calculated result (M) from the monitor processor 34 by apredetermined upper range limit, as determined at step 210, and if thecalculated result (C) is not less than the calculated result (M) by apredetermined lower range limit, as determined at step 212, then theprocedure 200 returns to step 204 to wait for the end of the nextactivation. Negative determination at steps 210 and 212 indicateacceptable functionality. On the other hand, if the two calculatedresults (C) and (M) are not within an acceptable tolerance of eachother, as determined at steps 210 and 212, then an appropriate errorhandling procedure is performed at step 214.

The error handling procedure may log or count each occurrence of theerror, alert the surgeon, shut down the electrosurgical generator and/ortake any other appropriate responsive measures. Counting the occurrenceof errors may enable other responsive measures after a certain number orthreshold of errors occurs sequentially or some number of errors occurswithin a larger number of activations or attempts to activate, forexample, 5 errors out of 10 attempted activations. If the error responsedoes not include shutting down the electrosurgical generator, asdetermined at step 216, then the procedure 200 returns to step 204 towait for the end of presently occurring activation. If, on the otherhand, the response does include shutting down the electrosurgicalgenerator, as determined at step 216, then a command to shut down theelectrosurgical generator is issued at step 218, and the procedure 200ends at step 220.

The present invention offers the improvement and advantage ofdetermining when a sensor fails. In such circumstances, the current orvoltage sense signal from the failed sensor will result in apower-related calculation which does not compare favorably with theother power-related calculation, thereby indicating a safety-relatedissue with the electrosurgical generator. Additionally, the presentinvention can detect whether there is a failure in certain othercomponents associated with the control and monitor microprocessors. Sucha failure would also result in a discrepancy between the calculatedresults because the failed component will generally not properly pass orhandle the value of the voltage and current signals which flow throughthat failed component. Moreover, should either of the controller ormonitor processors fail to execute their programed functionality, such afailure is also likely to be reflected in erroneous calculations of thepower-related information.

The present invention is particularly advantageous in combination whenthe monitor processor 34 monitors the mode functionality of theelectrosurgical generator 20 (FIG. 1). The second aforementioned patentapplication describes a mode functionality check incorporated in theelectrosurgical generator 20. In general terms, the mode functionalitycheck involves observing the characteristics of the drive-definingsignal 80 supplied by the control processor 32 to determine whether thecontrol processor 32 is delivering the proper pattern of drive signalsindicated by the selected mode of operation. If the characteristics ofthe drive-defining signal 80 are not consistent with the selected modeof operation, the monitor processor 34 terminates the delivery ofelectrosurgical power. For example, acceptable power calculations couldbe obtained even though the electrosurgical generator is operating in anincorrect mode. Since a malfunction could cause an error either in thepower delivered or the pattern of drive signals relative to the selectedmode of operation, checking both the power delivered and the modeinformation provides an very effective technique for determining theproper operation of the electrosurgical generator.

Many other benefits, advantages and improvements in monitoring theproper functionality of the electrosurgical generator will also beapparent upon gaining a full appreciation of the present invention.Thus, the electrosurgical generator can be prevented from operatingunder conditions which might possibly cause a risk to the patient andunder conditions where the output power and performance of theelectrosurgical generator is more reliably delivered.

Presently preferred embodiments of the invention and its improvementshave been described with a degree of particularity. This description hasbeen made by way of preferred example. It should be understood that thescope of the invention is defined by the following claims.

1. An electrosurgical generator which delivers electrosurgical outputpower and which regulates the amount of output power delivered fromfeedback information, comprising: a plurality of sensors connected tosense current and voltage of the output power delivered and operative tosupply current and voltage measurement signals related to the amount ofcurrent and voltage sensed; a control processor receptive of the currentand voltage measurement signals and which performs a first computationbased on the current and voltage measurement signals to derive thefeedback information and to derive a first value related to the outputpower delivered; a monitor processor receptive of the current andvoltage measurement signals and which performs a second computationseparate from the first computation to derive a second value related tothe output power delivered; a communication path connecting the controland monitor processors over which the control and monitor processorscommunicate information including the first and second values, one ofthe control or monitor processors receiving the first and second valuesbeing a comparison processor; the comparison processor executing acomparison procedure for comparing the first and second values anddelivering an error condition signal when the first and second valuesdiffer by a predetermined amount; and the electrosurgical generatorresponding to the assertion of the error condition signal by one ofeither issuing an error indication or terminating the delivery of outputpower.
 2. An electrosurgical generator as defined in claim 2, whereinthe plurality of sensors includes: a first current sensor for supplyinga first current sense measurement signal used in performing the firstcomputation; a second current sensor for supplying a second currentsense measurement signal used in performing the second computation; afirst voltage sensor for supplying a first voltage sense measurementsignal used in performing the first computation; and a second voltagesensor for supplying a second voltage sense measurement signal used inperforming the second computation.
 3. An electrosurgical generator asdefined in claim 2, wherein the control and monitor processors aredigital processors.
 4. An electrosurgical generator as defined in claim3, further comprising: a first analog to digital converter (ADC)connected to the first current and voltage sensors and operative toconvert the first current and voltage sense measurement signals,respectively, into digital form; a first direct memory access (DMA)controller; a first buffer connected to the first ADC and to the firstDMA controller, the first DMA controller placing the digital form of thefirst current and voltage sense measurement signals into the firstbuffer; the control processor connected to the first buffer to read thedigital form of the first current and voltage sense measurement signalsfrom the first buffer to perform the first computation; a second analogto digital converter (ADC) connected to the second current and voltagesensors and operative to convert the second current and voltage sensemeasurement signals, respectively, into digital form; a second directmemory access (DMA) controller; a second buffer connected to the secondADC and to the second DMA controller, the second DMA controller placingthe digital form of the second current and voltage sense measurementsignals into the second buffer; and the monitor processor connected tothe second buffer to read the digital form of the second current andvoltage sense measurement signals from the second buffer to perform thesecond computation.
 5. An electrosurgical generator as defined in claim1, further comprising: a system processor which oversees functionalityof the control and monitor processors, the system processor connected tothe communication path to communicate with the control and monitorprocessors, the system processor rather than the monitor or controlprocessors being the comparison processor which issues the errorindication.
 6. An electrosurgical generator as defined in claim 5,wherein: the control processor executes the first calculation; themonitor processor executes the second calculation; and the control andmonitor processors send the first and second values to the systemprocessor over the communication path.
 7. An electrosurgical generatoras defined in claim 5, further comprising: an alarm connected to thesystem processor and responsive to the error condition signal to deliveran alarm.
 8. An electrosurgical generator as defined in claim 5,wherein: the system controller responding to the assertion of the errorcondition signal by logging an error occurrence.
 9. A method as definedin claim 5, wherein: the system processor responds to the errorcondition signal by incrementing a count number with each instance wherethe first and second values differ by more than the predeterminedamount; the system processor indicates the error condition upon thecount number reaching a predetermined threshold.
 10. A method as definedin claim 9, wherein: the system processor resets the count number to apredetermined count value upon the first and second values not differingby the predetermined amount within a predetermined number of most recentcomparisons.
 11. A method as defined in claim 9, wherein: the systemprocessor increments the count number only with each instance where thefirst and second values differ by the predetermined amount within apredetermined number of most recent comparisons.
 12. A method ofevaluating functionality of an electrosurgical generator which deliverselectrosurgical output power established by an output current and anoutput voltage, comprising: sensing the output voltage and the outputcurrent; calculating with a first computation a first value related tothe output power delivered by using the sensed output current and thesensed output voltage; calculating with a second computation separatefrom the first computation a second value related to the output powerdelivered by using the sensed output current and the sensed outputvoltage; comparing the first and second values; and indicating an errorcondition when the first and second values differ by a predeterminedamount.
 13. A method as defined in claim 1, further comprising: sensingthe output voltage and the output current separately for use in thefirst and second computations; and calculating the first value usingvalues of the sensed output voltage and the sensed output current whichare separate from values of the sensed output voltage and the sensedoutput current used in calculating the second value.
 14. A method asdefined in claim 13, further comprising: sensing the output current bysensing a plurality of current values for each of the first and secondcomputations; sensing the output voltage by sensing a plurality ofvoltage values for each of the first and second computations; performinga root mean square computation on each of the sensed pluralities ofcurrent values and on each of the sensed pluralities of voltage valuesto obtain a root mean square current value of each of the pluralities ofsensed current values and to obtain a root mean square voltage value ofeach of the pluralities of sensed voltage values; and using the rootmean square current values and the root mean square voltage values inthe first and second computations to calculate the first and secondvalues.
 15. A method as defined in claim 13, wherein the electrosurgicalgenerator includes a control processor which controls the delivery ofthe electrosurgical output power and also includes a monitor processorwhich monitors functions of the electrosurgical generator, and furthercomprising: performing the first calculation using the controlprocessor; and performing the second calculation using the monitorprocessor.
 16. A method as defined in claim 12, further comprising:terminating delivery of the electrosurgical output power upon indicatingan error condition.
 17. A method as defined in claim 12, furthercomprising: incrementing a count number with each instance where thefirst and second values differ by more than the predetermined amount;and indicating the error condition upon the count number reaching apredetermined threshold.
 18. A method as defined in claim 17, furthercomprising: resetting the count number to a predetermined count valueupon the first and second values not differing by the predeterminedamount within a predetermined number of most recent comparisons.
 19. Amethod as defined in claim 17, further comprising: incrementing thecount number only with each instance where the first and second valuesdiffer by the predetermined amount within a predetermined number of mostrecent comparisons.